Pulsed time-of-flight laser range finder techniques for fast, high precision measurement applications

Abstract

This thesis describes the development of high bandwidth (~1 GHz) TOF (time-of-flight) laser range finder techniques for industrial measurement applications in the measurement range of zero to a few dozen metres to diffusely reflecting targets. The main goal has been to improve single-shot precision to mm-level in order to shorten the measurement result acquisition time. A TOF laser range finder consists of a laser transmitter, one or two receivers and timing discriminators, and a time measuring unit. In order to improve single-shot precision the slew-rate of the measurement pulse should be increased, so the optical pulse of the laser transmitter should be narrower and more powerful and the bandwidth of the receiver should be higher without increasing the noise level too much. In the transmitter usually avalanche transistors are used for generating the short (3–10 ns) and powerful (20–100 A) current pulses for the semiconductor laser. Several avalanche transistor types were compared and the optimization of the switching circuit was studied. It was shown that as high as 130 A current pulses are achievable using commercially available surface mount avalanche